This invention relates to a method of solution mining a soluble mineral from a subterranean deposit therof having an overlying water bearing formation. More particularly, this invention relates to the method of utilizing water from the water bearing formation to prevent plugging of a withdrawal conduit caused by precipitation of the mineral from the solution being withdrawn.
Subterranean deposits of soluble minerals of various descriptions can be recovered by solution mining. In a typical solution mining operation a salt is recovered from a deposit thereof by introducing through a conduit in a bore hole in communication with the deposit an aqueous solvent for the salt. A solution of the desired salts is formed as a cavity is created by the extraction of salt from the deposit and an enriched solution is withdrawn from the deposit through the same or a second bore hole. The withdrawn solution can be treated for the production of the desired salt from the solution. This technique has been used to recover salts such as sodium chloride and potassium chloride from such mineral deposits as kalinite, sylvinite, carnallite, and like salts using solvents such as water and solutions unsaturated with respect to the desired salts.
Solution mining is typically employed when the mineral deposit is at substantial depths below the surface of the earth, i.e., greater than about 100 meters below the surface of the earth. These deposits may be found in New Mexico, Utah, Northern United States, and Canada and are most frequently between about 100 meters and and about 1800 meters below the surface of the earth. Deposits of these aforementioned salts and other minerals are found in many other parts of the world as well.
During the solution mining of these minerals deposits, cavities having substantial dimensions are created. Consequently, even at high flow rates through the cavity, the solvent becomes saturated with respect to the mineral. But, as the solution is withdrawn from the cavity the mineral precipitates owing to a decreasing solution temperature or owing to other factors. Such precipitation can cause plugging of the withdrawal conduit such that the solution can no longer be withdrawn from the cavity, thus requiring a shutdown and reworking to remove the blockage before the solution mining operation can be resumed.
Known methods of reducing or avoiding plugging the withdrawal conduit include introducing a smaller conduit concentrically within the withdrawal conduit such that enough diluting liquid can be mixed with the solution being withdrawn such that no solubility is exceeded within the withdrawal conduit. Alternately, other substances such as steam can be introduced into the conduit in order to increase the solubility of the mineral as the solution is withdrawn from the cavity.
Often these mineral deposits are overburded with water bearing formations or aquifers. Cavities in these deposits are solution mined in such a manner to avoid communication with the aquifers since this situation reduces the ability to pump fluid through the cavity. Further, the cavity solution is subject to contamination by minerals that often occur in these aquifers. When communication with the aquifer does occur, the practice is to minimize contamination of the cavity solution with a substantial amount of undesirable minerals by controlling the injection of solvent and withdrawal of solutions. Especially where the solvent is of a specifically designed composition to provide a selective extraction of specific minerals from the deposit, this contamination is particularly undesirable. Further, should uncontrollable amounts of water enter a cavity from the aquifer, undue dilution of product solution can occur rendering it impossible to economically recover the desired product.